I'll tag on to this post. I just picked up a M75 last month too, late 1945 right after they resumed production. I got mine from Rock Island Auction, it's actually nicer than I expected. Also right around $600 all in with cost, fees, and shipping. Has one little spot on side of barrel that got dinged/rubbed but other than that it looks like it's had little use, shoots like it too. Has original Lyman sights, I was able to get a new set of inserts for it too.
There was just a tiny amount of surface rust inside the wood on some of the small parts and screws. So I boiled all of it to convert. Rubbed the parts clean with a toothbrush and this is what they look like. Check out those beautiful screw heads.
Fine shooter. The center target was sighting it in (first time I shot it), then just shot some 5 round groups with various ammo. Prone, slinged-in, on the A-17 50-foot target.